Pharmacokinetic evidence for saturable renal tubular reabsorption of riboflavin

Pharmacokinetic relationships have been developed to characterize a multicompartment drug distribution and elimination model which includes a saturable renal tubular reabsorption process. The derived expressions have been applied to serum concentration and urinary excretion data obtained after rapid intravenous administration of riboflavin to man and dog. The mathematical relationships and experimental data demonstrate the dependence of renal clearance on the serum concentration of the drug and on urine flow rate. The results of this study indicate that the renal excretion of riboflavin, like that of several other water‐soluble vitamins, involves saturable tubular reabsorption as well as tubular secretion.